Multilayer circuit board manufacturing method

ABSTRACT

A method for manufacturing a multilayer circuit board containing a single-sided metal-clad laminate sheet and a substrate laminated together, the single-sided metal-clad laminate sheet containing a thermoplastic liquid crystal polymer film and a metal foil bonded to a surface of the thermoplastic liquid crystal polymer film, and the method containing:
         forming a laminate sheet having the thermoplastic liquid crystal polymer film and the metal foil bonded together; and heat treating the laminate sheet, wherein the heat treatment satisfies conditions (1) and (2) to manufacture the single-sided metal-clad laminate sheet:   (1) a heat treatment temperature ranges between 1° C. inclusive and 50° C. exclusive higher than a melting point of the thermoplastic liquid crystal polymer film, and   (2) a time for the heat treatment ranges from one second to 10 minutes.

TECHNICAL FIELD

The present invention relates to a method for manufacturing a metal-cladlaminate sheet including film (hereinafter referred to as “thermoplasticliquid crystal polymer film”) containing thermoplastic polymer(hereinafter referred to as “thermoplastic liquid crystal polymer”)capable of forming an optically anisotropic molten phase. The presentinvention also relates to a metal-clad laminate sheet manufactured bythis method.

BACKGROUND ART

Conventional metal-clad laminate sheets including thermoplastic liquidcrystal polymer film excel in low moisture absorbency, heat resistance,chemical resistance, and electrical properties derived fromthermoplastic liquid crystal polymer film, as well as in dimensionalstability. Thanks to such features, the metal-clad laminate sheets areused as a material for circuit boards including flexible wiring boardsand circuit boards for mounting semiconductors.

Of these metal-clad laminate sheets, for example, a proposed metal-cladlaminate sheet includes thermoplastic liquid crystal polymer film, and ametal foil (surface roughness: 2 μm to 4 μm) bonded to at least onesurface of the thermoplastic liquid crystal polymer film. A method formanufacturing the metal-clad laminate sheet includes, for example,thermocompression-bonding the thermoplastic liquid crystal polymer filmand the metal foil together between heating rolls with the thermoplasticliquid crystal polymer film kept under tension to obtain a laminatesheet, and heat-treating the laminate sheet at or above the meltingpoint of the thermoplastic liquid crystal polymer film. Here, thethermoplastic liquid crystal polymer film has a predeterminedorientation of molecules. Since such a metal-clad laminate sheetincludes a metal foil having great surface roughness, the providedmetal-clad laminate sheet may have high peel strength between the metalfoil and the thermoplastic liquid crystal polymer film. (See, forexample, PATENT DOCUMENT 1.)

CITATION LIST Patent Documents

PATENT DOCUMENT 1: Japanese Patent No. 4216433.

SUMMARY OF THE INVENTION Technical Problem

In recent years, common use of high-performance small electronics suchas smart phones encourages development of parts with high density andimprovement in performance of the electronics. Hence, there is a demandfor metal-clad laminate sheets with excellent peel strength betweenthermoplastic liquid crystal polymer film and a metal foil and capableof dealing with high-frequency transmission signals (i.e., having a highfrequency characteristic).

The metal-clad laminate sheet disclosed in PATENT DOCUMENT 1 excels inpeel strength between the thermoplastic liquid crystal polymer film andthe metal foil; however, the metal-clad laminate sheet lacks the highfrequency characteristic. This is problematic because it is difficult tobalance an adhesion property and a high frequency characteristic.

A high frequency characteristic of a metal foil acting as a transmissionline; that is an insertion loss, depends on a skin effect (a surfaceresistance) of the metal foil. Thus, the high frequency characteristicdepends on a surface shape, in particular surface roughness (a ten pointaverage surface roughness) Rz of the metal foil. A metal foil with agreat Rz and high roughness has a high insertion loss, causingdeterioration in high frequency characteristic; whereas, a metal foilwith a small Rz and low roughness has a low insertion loss, causingimprovement in high frequency characteristic. Hence, the metal foil witha small Rz and low roughness is desirable.

However, if the metal foil with low roughness is used to reduce aresistance of the skin effect and curb the insertion loss, the peelstrength between the metal foil and the thermoplastic liquid crystalpolymer film becomes insufficient. Despite various attempts to reducethe insertion loss and enhance the peel strength at the same time, noneof the attempts has successfully solved the problem.

The present invention is conceived in view of the above problem, andintended to provide a method for manufacturing a metal-clad laminatesheet which has a high frequency characteristic and excels in peelstrength between thermoplastic liquid crystal polymer film and a metalfoil. The present invention is also intended to provide a metal-cladlaminate sheet manufactured by the method.

Solution to the Problem

Inventors of the present invention have found out that when a metal foilhaving high roughness and thermoplastic liquid crystal polymer film arethermocompression-bonded together and heat-treated, peel strengthbetween the metal foil and the thermoplastic liquid crystal polymer filmcould increase. However, the inventors have found out that when a metalfoil having low roughness and thermoplastic liquid crystal polymer filmof the present invention are thermocompression-bonded together to form alaminate and the laminate is heat-treated, peel strength between themetal foil and the thermoplastic liquid crystal polymer film does notnecessarily increase. The inventors have further studied heat treatmentconditions of the laminate and found out that, to their surprise, thepeel strength increases when the heat treatment is continued until acertain time under a specific temperature condition, and decreases oncethe certain time has passed. Thus the inventors found out that the heattreatment temperature and the time condition are set within a specificrange, which successfully increases the peel strength of the laminateincluding the metal foil having low roughness and the thermoplasticliquid crystal polymer film thermocompression-bonded together. This ishow the inventors have come to the present invention.

Hence, the present invention provides a method for manufacturing ametal-clad laminate sheet including thermoplastic liquid crystal polymerfilm and a metal foil bonded to at least one surface of thethermoplastic liquid crystal polymer film. The method includes providinga heat treatment which satisfies conditions (1) and (2) below:

(1) a heat treatment temperature ranges between 1° C. inclusive and 50°C. exclusive higher than a melting point of the thermoplastic liquidcrystal polymer film; and(2) a time for the heat treatment ranges from one second to 10 minutes.

Moreover, a metal-clad laminate sheet of the present invention includesthermoplastic liquid crystal polymer film and a metal foil bonded to atleast one surface of the thermoplastic liquid crystal polymer film. Thethermoplastic liquid crystal polymer film is provided with a skin layerhaving a thickness below or equal to a surface roughness of the metalfoil.

The present invention provides a method for manufacturing a multilayercircuit board including a single-sided metal-clad laminate sheet and asubstrate laminated together, the single-sided metal-clad laminate sheetincluding thermoplastic liquid crystal polymer film and a metal foilbonded to a surface of the thermoplastic liquid crystal polymer film,and the method comprising: forming a laminate sheet having thethermoplastic liquid crystal polymer film and the metal foil bondedtogether; and providing the laminate sheet with a heat treatment whichsatisfies conditions (1) and (2) below to manufacture the single-sidedmetal-clad laminate sheet.

(1) A heat treatment temperature ranges between 1° C. inclusive and 50°C. exclusive higher than a melting point of the thermoplastic liquidcrystal polymer film.

(2) A lime for the heat treatment ranges from one second to 10 minutes.

Advantages of the Invention

The present invention can provide a metal-clad laminate sheet which hasa high frequency characteristic and excels in peel strength. Inparticular, under the conditions of the present invention, a metal-cladlaminate sheet provided in the present invention successfully hassufficient peel strength even when thermoplastic liquid crystal polymerfilm is laminated on a shiny side (i.e., a face not roughened) of ametal foil.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating a structure of ametal-clad laminate sheet according to an embodiment of the presentinvention.

FIG. 2 is a cross-sectional view illustrating a structure of themetal-clad laminate sheet that is heat-treated according to theembodiment of the present invention.

FIG. 3 is a schematic view illustrating an overall configuration of acontinuous hot-press apparatus to be used in a method for manufacturingthe metal-clad laminate sheet according to the embodiment of the presentinvention.

FIG. 4 is a cross-sectional view illustrating a structure of ametal-clad laminate sheet according to a modification of the presentinvention.

FIG. 5 is a schematic view illustrating an overall configuration of acontinuous hot-press apparatus to be used in a method for manufacturingthe metal-clad laminate sheet according to the modification of thepresent invention.

FIG. 6 is a cross-sectional view illustrating a structure of amultilayer circuit board including a single-sided metal-clad laminatesheet and a circuit board laminated together according to a modificationof the present invention.

FIG. 7 is a cross-sectional view illustrating a method for manufacturingthe multilayer circuit board according to the modification of thepresent invention.

FIG. 8 is a cross-sectional view illustrating a method for manufacturinga multilayer circuit board according to a modification of the presentinvention.

FIG. 9 is a cross-sectional view illustrating a structure of themultilayer circuit board including a single-sided metal-clad laminatesheet and a circuit board laminated together according to themodification of the present invention.

FIG. 10 is a cross-sectional view illustrating a method formanufacturing a multilayer circuit board according to a modification ofthe present invention.

FIG. 11 is a cross-sectional view illustrating a structure of themultilayer circuit board including a single-sided metal-clad laminatesheet and a film substrate laminated together according to themodification of the present invention.

FIG. 12 is a scanning electron micrograph (SEM) of a metal-clad laminatesheet (before heat treatment) according to Example 30.

FIG. 13 is a scanning electron micrograph (SEM) of the metal-cladlaminate sheet (after heat treatment) according to Example 30.

FIG. 14 is a cross-sectional view illustrating a structure of aconventional metal-clad laminate sheet.

DETAILED DESCRIPTION

An embodiment of the present invention will be described in detailbelow, with reference to the drawings. The present invention is notlimited to the embodiment below.

FIG. 1 is a cross-sectional view illustrating a structure of ametal-clad laminate sheet according to an embodiment of the presentinvention.

As illustrated in FIG. 1, a metal-clad laminate sheet 1 of thisembodiment includes a thermoplastic liquid crystal polymer film 2 and ametal foil 3 laminated on one surface of the thermoplastic liquidcrystal polymer film 2.

<Metal Foil>

The metal foil 3 of the present invention may be any given metal foil.Examples of the metal foil 3 are copper, gold, silver, nickel, aluminum,and stainless steel. Beneficially, the metal foil 3 may be a copper foiland a stainless-steel foil in view of electrical conductivity, handling,and costs. Note that the copper foil may be manufactured by rolling andelectrolysis.

Furthermore, the metal foil 3 may beneficially be chemically treated,such as acid cleaning commonly provided to a copper foil. Moreover, themetal foil 3 may beneficially have a thickness ranging from 9 μm to 200μm, and more beneficially from 9 μm to 40 μm.

This is because if the metal foil 3 is thinner than 9 μm, the thicknessis insufficient so that the metal foil 3 could be deformed to have, forexample, a wrinkle in a manufacturing process of the metal-clad laminatesheet 1. If the metal foil 3 is thicker than 200 μm, the thickness isexcessive so that, when the metal foil 3 is used as a flexible wiringboard, the flexible wiring board could be hard to bend.

Moreover, in the present invention, the metal foil 3 may beneficiallyhave small surface roughness (i.e., low roughness), and in particular,have a ten point average surface roughness Rz of smaller than 2.0 μm inview of an excellent high frequency characteristic. In addition, themetal foil 3 may be 1.5 μm or thinner, and in particular, 1.1 μm orthinner in view of a balance between a high frequency characteristic andpeel strength. It is conventionally difficult to bond metal foil tothermoplastic liquid crystal polymer film when a bonding face of themetal foil is not roughened (a shiny side). However it is presentlysurprising that the present invention achieves excellent peel strengtheven though such a shiny side of the metal foil is laminated on thethermoplastic liquid crystal polymer film. The metal foil can belaminated when the shiny side has a roughness of 0.5 μm or lower to 0.3μm.

Note that when the metal foil has a surface roughness of 2.0 μm orgreater, the lamination could cause a rough texture on the surface ofthe metal foil roughened to penetrate a film skin layer inherent in athermoplastic liquid crystal polymer film, and to reach a core layerinside the film. Hence even though the peel strength between thethermoplastic liquid crystal polymer film and the metal foil improves,it is difficult to achieve an excellent high frequency characteristic.

Specifically, metal foil to be used as the metal foil 3 has a surfaceroughness Rz of smaller than 2.0 μm, which exhibits an excellent highfrequency characteristic. This is why the metal-clad laminate sheet 1having excellent peel strength can be obtained.

Note that the “surface roughness” here is a ten point average surfaceroughness (Rz) of the metal foil measured with a contact surfaceroughness meter (manufactured by Mitsutoyo Corporation Ltd., Model:SJ-201). The surface roughness is roughness of a surface, of the metalfoil 3, which makes contact with the thermoplastic liquid crystalpolymer film 2.

Furthermore, the surface roughness is measured with a technique incompliance with ISO 4287-1997. More specifically, the surface roughness(Rz) is obtained as follows: A reference length is extracted from aroughness curve along an average line of the roughness curve. The sum ofthe average value of the top five heights (peaks of the convex curves)and the average value of the bottom five depths (bottoms of the concavecurves) is represented in micrometers to be a ten point average surfaceroughness.

In general, commercially available metal foil has a surface roughened toenhance peel strength to, for example, resin film for lamination. In thepresent invention, such enhanced peel strength may be achieved even whena shiny side of metal foil, not roughened and having small surfaceroughness, and thermoplastic liquid crystal polymer film are laminatedtogether. Thus, the present invention may implement a metal-cladlaminate sheet which excels in high frequency characteristic, thanks tothe low roughness of the metal foil, and may enhance the peel strengtheven if the surface of the metal foil is not roughened. Such featuresmay improve work efficiency and reduce costs.

<Thermoplastic Liquid Crystal Polymer Film>

Materials for the thermoplastic liquid crystal polymer film of thepresent invention are not limited to any particular ones. Examples ofthe materials may be known thermotropic liquid crystal polyester andthermotropic liquid crystal polyester amid derived from compoundsclassified into (1) to (4) illustrated as examples below and derivativesof the compounds. As a matter of course, the material compounds may becombined within an appropriate scope in order to obtain polymer capableof forming an optically anisotropic molten phase.

(1) Aromatic or Aliphatic Dihydroxy Compound. (See Table 1 for TypicalExamples.)

TABLE 1 Chemical Structural Formulas for Typical Examples of Aromatic orAliphatic Dihydroxy Compound

HO(CH₂)_(n)OH (n is an integer from 2 to 12.)

(2) Aromatic or Aliphatic Dicarboxylic Acid. (See Table 2 for TypicalExamples.)

TABLE 2 Chemical Structural Formulas for Typical Examples of Aromatic orAliphatic Dicarboxylic Acid

HOOC(CH₂)_(n)COOH (n is an integer from 2 to 12.)

(3) Aromatic Hydroxycarboxylic Acid (See Table 3 for Typical Examples.)

TABLE 3 Chemical Structural Formulas for Typical Examples of AromaticHydroxycarboxylic Acid

(4) Aromatic Diamine, Aromatic Hydroxyamine, or Aromatic AminocarboxylicAcid (See Table 4 for Typical Examples.)

TABLE 4 Chemical Structural Formulas for Typical Examples of AromaticDiamine, Aromatic Hydroxyamine, or Aromatic Aminocarboxylic Acid

Moreover, typical examples of the thermoplastic liquid crystal polymerto be obtained as these material compounds include copolymers (a) to (e)having structure units illustrated in Table 5.

TABLE 5 Typical Examples of Thermoplastic Liquid Crystal Polymer

(a)

(b)

(c)

(d)

(e)

Furthermore, the thermoplastic liquid crystal polymer to be used for thepresent invention beneficially has a melting point ranging approximatelyfrom 200° C. to 400° C., in particular, approximately from 250° C. to300° C. in order to provide the film with desired heat resistance andworkability. In view of manufacturing the film, however, thethermoplastic liquid crystal polymer beneficially has a relatively lowmelting point.

Hence, when the heat resistance and the melting point need to be higher,the film obtained already is heat-treated so that the heat resistanceand the melting point may be raised to a desired degree. As an exampleof a condition for a heat treatment, when film already obtained has amelting point of 283° C., the melting point will rise to 320° C. if thefilm is heated at 260° C. for five hours.

The thermoplastic liquid crystal polymer film 2 of the present inventionis obtained when the above polymer is extruded. Here, the polymer may beextruded by any technique. Well-known techniques such as T-dieextrusion, stretching a laminated body, and inflation are industriallyadvantageous. In particular, in the inflation, stress is applied notonly in a machine axis (longitudinal) direction (hereinafter referred toas an “MD” direction) of the film, but also in a direction perpendicularto the MD direction (hereinafter referred to as a “TD” direction).Hence, the obtained film is well balanced between mechanical and thermalproperties in the MD and TD directions.

Moreover, the thermoplastic liquid crystal polymer film 2 of thisembodiment beneficially has an orientation of molecules (SOR: SegmentOrientation Ratio) between 0.90 or above and below 1.20, beneficially0.95 or above and 1.15 or below, and more beneficially 0.97 or above and1.15 or below in the film MD direction.

The thermoplastic liquid crystal polymer film 2 whose orientation ofmolecules is within this range is well-balanced between mechanical andthermal properties in the MD and TD directions. Thanks to such afeature, the thermoplastic liquid crystal polymer film 2 is not onlypractical but also, as described above, provides the metal-clad laminatesheet 1 for a circuit board with good isotropy and dimensionalstability.

Moreover, when the orientation of molecules SOR is 0.50 or below or 1.50or above, the orientation of the liquid crystal polymer molecules isexcessively biased so that the film becomes hard and susceptible to betorn in the TD direction or the MD direction. For the use of circuitboards, which requires morphological stability such as no warping whenheated, the orientation of molecules SOR needs to be 0.90 or above andbelow 1.15. In particular, the orientation of molecules SOR is desirably0.90 or above and 1.08 or below if the warping when heated is to becompletely eliminated. Moreover, when the orientation of molecules isset to 0.90 or above and 1.08 or below, a permittivity of the film maybecome constant.

Here, the “orientation of molecules SOR” is an index to provide a degreeof a molecular orientation to a segment included in molecules. Incontrast to a conventional molecular orientation ratio (MOR), theorientation of molecules SOR is determined on the ground of a thicknessof an object.

Moreover, the above orientation of molecules SOR is calculated below.

First, using a well-known a microwave molecular orientation measurementdevice, the thermoplastic liquid crystal polymer film 2 is inserted intoa microwave resonant waveguide of the device so that the film face isperpendicular to a traveling direction of the microwave. The devicemeasures electric field strength of the microwave (transmission strengthof a microwave) transmitted through this film.

Then, based on this measured value, a value m (referred to as arefractive index) is calculated by Math. 1 below.

(Math. 1)

m=(Zo/Δz)×[1−vmax/vo]  (1)

where Zo is a device constant, Δz is an average thickness of an object,vmax is an oscillation frequency to provide the maximum microwavetransmission strength when a microwave oscillation frequency is changed,and vo is an oscillation frequency to provide the maximum microwavetransmission strength when the average thickness is zero (i.e., when noobject is found).

Next, the orientation of molecules SOR is calculated by m0/m90 where:(i) m0 is a value of m when a rotation angle with respect to anoscillation direction of the microwave is 0° (i.e., when the oscillationdirection of the microwave matches a direction in which molecules of theobject are most appropriately oriented (generally the MD direction ofthe extruded film), and the minimum microwave transmission strength isprovided; and (ii) m90 is a value of m when the rotation angle is 90.

The thickness of the thermoplastic liquid crystal polymer film 2 of thepresent invention is not limited to a particular thickness. When themetal-clad laminate sheet 1, including the thermoplastic liquid crystalpolymer film 2 as an electrically insulating material, is used as awiring board, the thickness beneficially ranges from 20 μm to 500 μm,more beneficially from 20 μm to 150 μm, still more beneficially from 20μm to 100 μm, and most beneficially from 20 μm to 50 μm.

This is because when the thickness of the film is excessively thin, therigidity and strength of the film become small. When an electronic partis mounted on a printed wiring board to be obtained, this excessivelythin film causes deformation of the printed wiring board due toapplication of pressure, followed by deterioration of precision inwiring position to cause malfunction.

Moreover, the thermoplastic liquid crystal polymer film 2 has acoefficient of thermal expansion beneficially ranging from 10 ppm/° C.to 30 ppm/° C., more beneficially from 12 ppm/° C. to 25 ppm/° C., andfurther beneficially from 15 ppm/° C. to 20 ppm/° C. This is because,when a circuit is formed on the metal-clad laminate sheet, the filmcould (i) contract if the coefficient of thermal expansion is smallerthan 10 ppm/° C., and (ii) expand if the coefficient of thermalexpansion is greater than 30 ppm/° C. Note that the coefficient ofthermal expansion is a value to be measured by a technique described inExamples later. Beneficially, the thermoplastic liquid crystal polymerfilm 2 has a coefficient of thermal expansion ranging from 10 ppm/° C.to 30 ppm/° C. because the metal-clad laminate sheet 1 has a smalldimensional variation.

Furthermore, the dimensional stability (occurrence of distortion) of themetal-clad laminate sheet 1 may be determined using, as an index, adimensional variation based on a metal-clad laminate sheet with metalfoil and a metal-clad laminate sheet without metal foil. If thedimensional variation is not over ±0.1%, the occurrence of distortion inthe metal-clad laminate sheet 1 is reduced.

Note that the “dimensional variation” here is obtained as follows:Reference points in the MD and TD directions are determined on theheat-treated metal-clad laminate sheet by a technique in compliance withIPC-TM6502.2.4. After the metal foil is etched, the metal-clad laminatesheet 1 is baked at 150° C. for 30 minutes. Rates of variation indimension (%) in the MD and TD directions are measured based on thepositions of the reference points after the baking. The average value ofthe measured rates of variation in dimension is the “dimensionalvariation”.

As an electrically insulating material for a main circuit board of apersonal computer, a complex of the above thermoplastic liquid crystalpolymer film and another electrically insulating material such as aglass-based material may be used. Note that the film may contain anadditive such as a lubricant and an antioxidant.

Described next is a method for manufacturing a metal-clad laminate sheetaccording to an embodiment of the present invention.

The manufacturing method according to this embodiment includes: forminga laminate sheet having the thermoplastic liquid crystal polymer film 2and the metal foil 3 bonded together; and providing the laminate sheetwith heat treatment.

<Forming Laminate Sheet>

First, the thermoplastic liquid crystal polymer film 2 elongated isplaced in a state of tension. On one face of the thermoplastic liquidcrystal polymer film 2, the metal foil 3 elongated is laid. Thethermoplastic liquid crystal polymer film 2 and the metal foil 3 arethermocompression-bonded between heating rolls and laminated together.

Note that the “state of tension” here is that a tensile force rangingfrom 0.12 kg/mm² to 0.28 kg/mm², for example, is applied to the film inthe film MD direction (a direction of tension).

FIG. 3 is a schematic view illustrating an overall configuration of acontinuous hot-press apparatus to be used in a method for manufacturinga metal-clad laminate sheet according to an embodiment of the presentinvention.

This continuous hot-press apparatus 10 is for manufacturing asingle-sided metal-clad laminate sheet including the thermoplasticliquid crystal polymer film 2 and the metal foil 3 bonded to one of thesurfaces of the thermoplastic liquid crystal polymer film 2. Asillustrated in FIG. 3, the continuous hot-press apparatus 10 includes adelivery roll 4 loaded with the thermoplastic liquid crystal polymerfilm 2 in a roll shape, a delivery roll 5 loaded with the metal foil 3such as copper foil in a roll shape, and a heating roll 7 bonding thethermoplastic liquid crystal polymer film 2 and the metal foil 3together by thermocompression-bonding to form the laminate sheet 6.

When a single-sided metal-clad laminate sheet is manufactured, examplesof the heating roll 7 include a pair of a heat-resistant rubber roll 8and a heating metal roll 9 (both of which have a roll face hardnessdegree of 80 or above). Beneficially, the heat-resistant rubber roll 8is positioned close to the thermoplastic liquid crystal polymer film 2,and the heating metal roll 9 is positioned close to the metal foil 3.

In accordance with a test to be carried out beneficially with a type-Aspring-loaded hardness testing machine in compliance with JIS K 6301,the heat-resistant rubber roll 8 to be used in manufacturing asingle-sided metal-clad laminate sheet beneficially has a roll facehardness degree of 80 or above, and more beneficially ranging from aroll face hardness degree of 80 to 95. Here, if the hardness degree isbelow 80, pressure in thermocompression bonding is insufficient, and sois peel strength of the laminate sheet 6. Furthermore, if the hardnessdegree exceeds 95, locally linear pressure acts between theheat-resistant rubber roll 8 and the heating metal roll 9. This couldgive the laminate sheet 6 poor appearance. Note that rubber having thehardness of 80 or above may be obtained when a vulcanization acceleratorsuch as a vulcanizing agent and an alkaline material is added tosynthetic rubber such as silicone rubber and fluorinated rubber ornatural rubber.

Then, as illustrated in FIG. 1, the thermoplastic liquid crystal polymerfilm 2 and the metal foil 3 are laid one on top of the other,transported in the film MD direction, and supplied between a pair of theheat-resistant rubber roll 8 and the heating metal roll 9. Then, thethermoplastic liquid crystal polymer film 2 and the metal foil 3 arethermocompression-bonded and laminated together.

<Heat Treating>

Next the obtained laminate sheet 6 is heat-treated so that themetal-clad laminate sheet 1 is produced. As illustrated in FIG. 3, thecontinuous hot-press apparatus 10 includes: a nip roll 11 fortransporting the laminate sheet 6; a heat treatment unit 12 forheat-treating the laminate sheet 6; and a wind-up roll 13 for winding upthe heat-treated metal-clad laminate sheet 1.

The heat treatment unit 12 may be any given unit if the unit provides aheat treatment to the laminate sheet 6 at a melting point of thethermoplastic liquid crystal polymer film 2 or above. Examples of theheat treatment unit 12 include a hot-air heat treatment furnace, ahot-air circulation-type dryer, a heating roll, a ceramic heater, a heattreatment unit using a far-infrared ray, and a method using acombination thereof. Moreover, in view of reducing oxidization of asurface of the metal foil 3, heated nitrogen gas is used to heat-treatthe laminate sheet 6 under an inert atmosphere having an oxygenconcentration of 0.1% or below.

Here, where Tm (° C.) is a melting point of the thermoplastic liquidcrystal polymer film 2 and Ta (° C.) is a heat treatment temperature, afeature of the present invention is that the laminate sheet 6 isheat-treated for one second to 10 minutes at the temperature Ta rangingbetween 1° C. inclusive and 50° C. exclusive higher than the meltingpoint Tm of the thermoplastic liquid crystal polymer film.

Such a heat treatment to the laminate sheet 6 may enhance the peelstrength between a metal foil having low roughness and thermoplasticliquid crystal polymer film, which has conventionally been difficult. Inparticular, the peel strength is enhanced between thermoplastic liquidcrystal polymer film and metal foil having a surface roughness Rz ofsmaller than 2.0 μm which excels in high frequency characteristic.

This heat treatment technique makes it possible to sufficiently improvepeel strength between thermoplastic liquid crystal polymer film and anon-roughened shiny side of metal foil which has conventionally hinderedsuch peel strength to the thermoplastic liquid crystal polymer film.

Note that, in view of further improving the peel strength between thethermoplastic liquid crystal polymer film 2 and the metal foil 3, theheat treatment temperature Ta may beneficially be set to a temperatureranging from 1° C. to 30° C., and more beneficially ranging from 2° C.to 30° C., higher than the melting point Tm of the thermoplastic liquidcrystal polymer film. Moreover, in a similar view point, the heattreatment time is beneficially set to five seconds to eight minutes,more beneficially to eight seconds to five minutes, and further morebeneficially to eight seconds to three minutes.

Furthermore, under the above heat treatment condition, the peel strengthbetween metal foil having low roughness and thermoplastic liquid crystalpolymer film is inferred to improve because of the reason below. Whenthe thermoplastic liquid crystal polymer film is usuallythermocompression-bonded to the metal foil, a surface of thethermoplastic liquid crystal polymer film melts by the heat of thethermocompression-bonding, and an orientation of molecules referred toas a skin layer appears on the surface by the pressure in thethermocompression-bonding.

As illustrated in FIG. 14, in a conventional metal-clad laminate sheet50, a skin layer 52 of a thermoplastic liquid crystal polymer film 51 issusceptible to a tear in one direction structure-wise compared with acore layer 53 within the film, and the skin layer 52 is different alsoin crystalline structure from the core layer 53. Hence, the interfaceadhesion between the core layer 53 and the skin layer 52 is weak suchthat the core layer 53 and the skin layer 52 are susceptible todelamination at the interface. That is why this skin layer 52 reducesthe peel strength between the thermoplastic liquid crystal polymer film51 and a metal foil 54 even though a convex protrusion 55 of the metalfoil 54 reaches the skin layer 52.

In this embodiment, however, the thermoplastic liquid crystal polymerfilm 2 and the metal foil 3 are thermocompression-bonded together and,with no pressure applied, heat-treated at a temperature higher than orequal to the melting point of the thermoplastic liquid crystal polymerfilm 2. Hence, the once formed orientation of the skin layer disappears(i.e., the factor to reduce the peel strength disappears), and the skinlayer 16 becomes thinner. Accordingly, as illustrated in FIG. 2, aconvex protrusion 18 of the metal foil 3 penetrates the skin layer 16and reaches the core layer 17. As a result, the peel strength is thoughtto improve.

Specifically, in the present invention, the thermoplastic liquid crystalpolymer film 2 and the metal foil 3 are thermocompression-bondedtogether and, with no pressure applied, heat-treated at a temperaturehigher than or equal to the melting point of the thermoplastic liquidcrystal polymer film 2. Hence, the thickness of the skin layer 16 of thethermoplastic liquid crystal polymer film 2 may be set below or equal tothe surface roughness of the metal foil 3. As a result, regardless ofthe surface roughness of the metal foil 3, the obtained metal-cladlaminate sheet 1 may have sufficient peel strength even though theroughness of the metal foil 3 is low.

Here, the thickness of the skin layer 16 is defined by a distancebetween (i) a boundary interface 19 between the skin layer 16 and thecore layer 17 and (ii) a surface 21, of the thermoplastic liquid crystalpolymer film 2, to the skin layer 16. The thickness of the skin layer 16of the present invention is an average value of thicknesses of any givenfive portions of the skin layer 16 within an area of 30 μm×30 μmobserved in a cross-section image.

Note that the boundary interface 19 between the skin layer 16 and thecore layer 17 is observed as a black cross section in the thermoplasticliquid crystal polymer film 2 when a cross section of the metal-cladlaminate sheet 1 is polished with a cross-section polisher and etchedwith a propylamine solution. This is because when the skin layer 16 isformed on the thermoplastic liquid crystal polymer film 2 by the heatand pressure generated in the thermocompression bonding, small domaingroups are formed between the skin layer 16 and the core layer 17. Thesesmall domain groups are dissolved and removed with the propylaminesolution, which is probably why the boundary interface 19 is observed asthe black cross section. Note that a scanning electron microscope issuitable as a unit for the observation.

Moreover, in view of peel strength, a thickness T of the skin layer 16is beneficially smaller than or equal to 95% of the surface roughness Rzof the metal foil 3 (i.e., T/Rz≤0.95), more beneficially smaller than orequal to 50%, and still more beneficially smaller than or equal to 20%.This is because when the thickness T is larger than 95% of the surfaceroughness Rz, the skin layer 16 and the core layer 17 may delaminatefrom each other at the interface.

Furthermore, as long as the thickness T of the skin layer 16 is smallerthan or equal to the surface roughness Rz, the thickness T of the skinlayer 16 may be larger than or equal to either 1% or 5% of the surfaceroughness Rz of the metal foil 3. Furthermore, for example, arelationship 0.05≤T/Rz≤0.95 may hold.

Moreover, in view of peel strength, the thickness of the skin layer 16may beneficially be 1.1 μm or smaller, more beneficially 0.9 μm orsmaller, and still more beneficially, 0.5 μm or smaller, and mostbeneficially 0.3 μm or smaller.

In addition, when metal foil with low roughness is used as the presentinvention shows, the peel strength increases to a peak and then startsto decrease if the heat treatment is continued. One of the reasons forthe decrease in the peel strength would be thermal degradation of thethermoplastic liquid crystal polymer film. However, such a phenomenondoes not occur when metal foil with high roughness is used.

Hence, a cause of this phenomenon was studied through an observation ofdelamination between a face of thermoplastic liquid crystal polymer filmand a face of metal foil in a laminate. Specifically, when a heattreatment was kept provided to the laminate, the peel strength onceincreased between the thermoplastic liquid crystal polymer film and themetal foil with low roughness decreased. The face of the filmdelaminated from the metal foil was observed in detail. The observationshowed that, of concave recesses and convex protrusions formed on thesurface of the metal foil, the convex protrusions were attached to theface of the film.

This result shows that, when the heat treatment is kept provided to thelaminate using the metal foil with low roughness, a cause of thephenomenon of the decrease in the peel strength could be thermaldegradation of the concave recesses and the convex protrusions on thesurface of the metal foil. Specifically, in the case of the metal foilwith low roughness, the convex protrusions are small in size andsusceptible to thermal degradation. In lamination, these convexprotrusions dig into the surface of the thermoplastic liquid crystalpolymer film to enhance the peel strength. Meanwhile, the convexprotrusions become brittle by heat, and tend to come off together withthe film when the film is delaminated from the metal foil. Hence,continuing the heat treatment could reduce the peel strength.

Meanwhile, metal foil with high roughness is originally high in peelstrength to the film. In addition, the convex protrusions on the surfaceof the metal foil are large in size. These convex protrusions aretolerant to heat and excel in resistance to thermal degradation,reducing thermal degradation of the surface of the metal foil due to theheat treatment. Despite the heat treatment contributing to the thermaldegradation of thermoplastic liquid crystal polymer film, no decrease inthe peel strength is thought to be observed.

Moreover, in the metal foil, the shiny side that is not roughened doesnot have any concave recesses or convex protrusions to be formed toincrease the peel strength. When the thermoplastic liquid crystalpolymer film is laminated on this shiny side, the decrease in the peelstrength by the heat treatment is also observed. This would be becauseof the following reason: In the peel strength between the thermoplasticliquid crystal polymer film and the shiny side with no roughness forincreasing the peel strength to the film provided, the thermaldegradation of the thermoplastic liquid crystal polymer film caused bythe continuing heat treatment is significantly reflected in the peelstrength. Hence the decrease in the peel strength is observed once acertain heat treatment time has passed.

As described above, under the heat treatment condition of the presentinvention, the difference in interface structure is eliminated (theinterface structure is homogenized) between the skin layer 16 and thecore layer 17 on the surface of the thermoplastic liquid crystal polymerfilm 2, so that the peel strength may be increased. In addition, sincethe heat treatment is provided under the condition in which the thermaldegradation does not occur to the surface of the metal foil 3 with lowroughness, the obtained laminate may have a high frequencycharacteristic and increased peel strength between the thermoplasticliquid crystal polymer film 2 and the metal foil 3.

Note that the heat treatment temperature Ta is set higher than themelting point Tm of the thermoplastic liquid crystal polymer film 2because, if the heat treatment temperature Ta is lower than or equal tothe melting point Tm, the effect of the disappearance of the skin layer16 on the surface of the thermoplastic liquid crystal polymer film 2 bythe heat treatment is insufficient such that the increase in the peelstrength is insufficient between the thermoplastic liquid crystalpolymer film 2 and the metal foil 3. If the heat treatment temperatureTa is set to 50° C. as high as or higher than the melting point Tm, theheat treatment temperature Ta rises close to the decompositiontemperature of the thermoplastic liquid crystal polymer film 2, suchthat the appearance of the metal-clad laminate sheet 1 could bedeteriorated with, for example, stain.

Such a heat treatment provided for a heat treatment time T may controlthe thermal degradations of the surface of the metal foil 3 with lowroughness and the thermoplastic liquid crystal polymer film 2. Thus, theobtained laminate may have a high frequency characteristic and increasedpeel strength between the thermoplastic liquid crystal polymer film 2and the metal foil 3.

Note that the skin layer of the present invention is a layer confirmedby an observation with a scanning electron microscope (SEM) when a crosssection of the metal-clad laminate sheet 1 is polished with across-section polisher and etched with a propylamine solution so thatthe structure of the domains is emphasized.

Moreover, the heat treatment of the present invention may control thecoefficient of thermal expansion of the thermoplastic liquid crystalpolymer film 2 within a specific range. For example, the heat treatmentover 10 minutes is not preferable because the coefficient of thermalexpansion of the thermoplastic liquid crystal polymer film 2 becomesexcessively high such that the dimensional variation of the metal-cladlaminate sheet 1 becomes inevitably high. Furthermore, when the heattreatment temperature Ta is higher than the melting point Tm of thethermoplastic liquid crystal polymer film 2, but not 1° C. as high asthe melting point Tm, the coefficient of thermal expansion of thethermoplastic liquid crystal polymer film 2 is low such that thedimensional variation of the metal-clad laminate sheet 1 becomesinevitably high. This is not preferable.

Note that the embodiment may be modified as described below.

The embodiment shows as an example of the metal-clad laminate sheet 1including the thermoplastic liquid crystal polymer film 2 and the metalfoil 3 bonded on one surface of the thermoplastic liquid crystal polymerfilm 2. The present invention may also be applied to the metal-cladlaminate sheet 1 in FIG. 4 including the thermoplastic liquid crystalpolymer film 2 and the metal foil 3 bonded on each side of thethermoplastic liquid crystal polymer film 2. Specifically the presentinvention may be applied to a metal-clad laminate sheet including thethermoplastic liquid crystal polymer film 2 and the metal foil 3 bondedat least on one surface of the thermoplastic liquid crystal polymer film2.

As illustrated in FIG. 5, used here is a continuous hot-press apparatus30; that is, the continuous hot-press apparatus 10 illustrated in FIG. 3further including another delivery roll loaded with another metal foil 3such as copper foil in a roll shape (in other words including twodelivery rolls 5).

Then, similar to the case of the above embodiment, first, thethermoplastic liquid crystal polymer film 2 elongated is placed in astate of tension. On each face of the thermoplastic liquid crystalpolymer film 2, the metal foil 3 elongated is laid. The thermoplasticliquid crystal polymer film 2 and the metal foil 3 arethermocompression-bonded between heating rolls 7 and laminated togetherso that a laminate sheet 15 is produced. Then, the obtained laminatesheet 15 is heat-treated so that a metal-clad laminate sheet 20 isproduced.

Then, similar to the case of the above embodiment, the heat treatmenttemperature Ta is set to range between 1° C. inclusive and 50° C.exclusive higher than the melting point Tm of the thermoplastic liquidcrystal polymer film 2, and the heat treatment is provided for onesecond to 10 minutes. As a result, the obtained metal-clad laminatesheet 20 may have a high frequency characteristic and increased peelstrength between the thermoplastic liquid crystal polymer film 2 and themetal foil 3.

Moreover, in a similar manner, the present invention is applicable to amultilayer circuit board 38 illustrated in FIG. 6 including thesingle-sided metal-clad laminate sheet 1, and a circuit board 36laminated together. The circuit board 36 includes the thermoplasticliquid crystal polymer film 2, the metal foil 3, and a circuit pattern37.

In this case, as illustrated in FIG. 7, the single-sided metal-cladlaminate sheet 1 and the circuit board 36 are laid on top of the otherand laminated together via a film face 35 of the single-sided metal-cladlaminate sheet 1 and a surface 28 of the circuit board 36 toward thecircuit pattern 37. Here, the surface 28 includes (i) a surface 40, ofthe thermoplastic liquid crystal polymer film 2, across from the metalfoil 3 in the circuit board 36, and (ii) a surface 27 of the circuitpattern 37 in the circuit board 36. With a vacuum batch-press machine,this laminate is heated and pressed by vacuum hot pressing so that thesingle-sided metal-clad laminate sheet 1 and the circuit board 36 arethermocompression-bonded together. As a result, the multilayer circuitboard 38 illustrated in FIG. 6 is produced.

Then, similar to the case of the above embodiment, the heat treatmenttemperature Ta is set to range between 1° C. inclusive and 50° C.exclusive higher than the melting point Tm of the thermoplastic liquidcrystal polymer film 2, and the heat treatment is provided for onesecond to 10 minutes. Hence, peel strength may be increased at aninterface 34 between the thermoplastic liquid crystal polymer film 2 andthe metal foil 3. In addition, peel strength may be increased at aninterface 50 between (i) the thermoplastic liquid crystal polymer film 2in the single-sided metal-clad laminate sheet 1 and (ii) thethermoplastic liquid crystal polymer film 2 and the circuit pattern 37in the circuit board 36. At the interface 50, a film face 35 of thesingle-sided metal-clad laminate sheet 1 and a surface 28 of the circuitboard 36 toward the circuit pattern 37 make contact with each other.

Moreover, as illustrated in FIG. 8, two single-sided metal-clad laminatesheets 1 illustrated in FIG. 1 are prepared, and laminated together viathe film face 35 on each single-sided metal-clad laminate sheet 1. As aresult, a multilayer circuit board 60 may be formed as illustrated inFIG. 9.

Then, also in this multilayer circuit board 60, peel strength may beincreased at the interface 34 between the thermoplastic liquid crystalpolymer film 2 and the metal foil 3 as seen in the above multilayercircuit board 38. In addition, peel strength may be increased at aninterface 71 between layers of the thermoplastic liquid crystal polymerfilm 2 included in the respective single-sided metal-clad laminatesheets 1. At the interface 71, the film faces 35 of the respectivesingle-sided metal-clad laminate sheets 1 make contact with each other.

Here, as illustrated in FIG. 8, two single-sided metal-clad laminatesheets 1 are laminated together via their respective film faces 35. Thislaminate is heated and pressed by vacuum hot pressing so that the twosingle-sided metal-clad laminate sheets 1 are thermocompression-bondedtogether. As a result, the multilayer circuit board 60 is formed asillustrated in FIG. 9.

Furthermore, as illustrated in FIG. 10, a film substrate 25 made of thethermoplastic liquid crystal polymer film 2 may be used instead of thecircuit board 36. Through a film face of the single-sided metal-cladlaminate sheet 1 illustrated in FIG. 11 and a film face 26 of the filmsubstrate 25, the single-sided metal-clad laminate sheet 1 and the filmsubstrate 25 are laminated together so that a multilayer circuit board61 may be formed as illustrated in FIG. 11.

Then, also in this multilayer circuit board 61, peel strength may beincreased at the interface 34 between the thermoplastic liquid crystalpolymer film 2 and the metal foil 3 as seen in the above multilayercircuit board 38. In addition, peel strength may be increased at an 13Sinterface 23 between the thermoplastic liquid crystal polymer film 2 inthe single-sided metal-clad laminate sheet 1 and the thermoplasticliquid crystal polymer film 2 in the film substrate 25. At the interface23, the film face 35 of the single-sided metal-clad laminate sheet 1 andthe film face 26 of the film substrate 25 make contact with each other.

Here, as illustrated in FIG. 10, the single-sided metal-clad laminatesheet 1 and the film substrate 25 are laid on top of the other andlaminated together via the film face 35 of the single-sided metal-cladlaminate sheets 1 and the film face 26 of the film substrate 25. Thislaminate is heated and pressed by vacuum hot pressing so that thesingle-sided metal-clad laminate sheets 1 and the film substrate 25 arethermocompression-bonded together. As a result, a multilayer circuitboard 61 is formed as illustrated in FIG. 11.

EXAMPLES

The present invention is described below based on examples. Note thatthe present invention shall not be limited to these examples. Theseexamples may be modified and changed based on the intent of the presentinvention. Such a change and modification shall not be excluded from thescope of the invention.

Examples 1 to 10, Comparative Examples 1 to 6

<Producing Thermoplastic Liquid Crystal Polymer Film>

Thermotropic liquid crystal polyester containing a 6-hydroxy-2-naphthoicacid unit (27 mol %) and a p-hydroxybenzoic acid unit (73 mol %) washeated at 280° C. to 300° C. and kneaded with a single screw extruder.Then, the thermotropic liquid crystal polyester was extruded from aninflation die having a diameter of 40 mm and a slit distance of 0.6 mmso that thermoplastic liquid crystal polymer film having a thickness of50 μm was obtained. This thermoplastic liquid crystal polymer film has amelting point Tm of 283° C. and a heat distortion temperature Tdef of230° C.

Note that the melting point was obtained with a differential scanningcalorimeter through an observation of a thermal behavior of the film.Specifically, the produced film was heated at a speed of 20° C./min tomelt completely. Then, the melt film was rapidly cooled to 50° C. at aspeed of 50° C./imin. Then, when the cooled film was heated again at aspeed of 20° C./min, the endothermic peak observed was determined as themelting point of the thermoplastic liquid crystal polymer film.

<Producing Metal-Clad Laminate Sheet>

Next, using a continuous hot-press apparatus, the produced thermoplasticliquid crystal polymer film and rolled copper foil having a thickness of12 μm (Manufactured by JX Nippon Mining & Metals Corporation, TradeName: BHYX-92F-HA, Surface Roughness: 0.9 μm) were introduced between aheat-resistant rubber roll and a heating metal roll and thermallypressed to bond together. Hence, a laminate sheet was produced.

Note that the surface roughness Rz of the copper foil was calculatedthrough measurement of ten point average surface roughness on aroughened face in compliance with JISB0601, using a surface roughnesstester (Manufactured by Mitsutoyo Corporation, Trade Name: SURF TESTSJ-201). Under a condition in which a measurement reference length was0.8 mm, an evaluation length was 4 mm, a cutoff value was 0.8 mm, and afeed speed was 0.5 mm/sec, the surface roughness was measured 10 timeswith the measurement position changed to be in parallel with the rollingdirection. An average value among the ten measurements was obtained.

As the heat-resistant rubber roll making contact with the thermoplasticliquid crystal polymer film, a resin-coated metal roll (Manufactured byYuri Roll Machine Co., Ltd., Trade Name: Super Ten Apex. ResinThickness: 1.7 cm) was used. The heat-resistant rubber roll and theheating metal roll used had a diameter of 40 cm.

A surface temperature of the heating metal roll was set to a temperature20° C. lower (i.e., 263° C.) than the melting point of the thermoplasticliquid crystal polymer film. A pressure to be applied to thethermoplastic liquid crystal polymer film and the copper foil betweenthe heat-resistant rubber roll and the heating metal roll was set to 120kg/cm² in face pressure. Under this condition, the thermoplastic liquidcrystal polymer film was moved along the heat-resistant rubber roll.Then, the copper foil was laid on, and temporarily bonded to, thethermoplastic liquid crystal polymer film.

<Heat Treading>

Next, winding tension was released on the production line with a niproll. The produced laminate sheet was passed through an infrared heattreatment apparatus (Manufactured by Noritake Co., Ltd., Trade Name:Roll to Roll Far-Infrared Heating Furnace) and heat-treated. Metal-cladlaminate sheets for Examples 1 to 10 and Comparative Examples 1 to 6were produced.

Note that a heat treatment time (i.e., a time period in which any givenone point of a laminate sheet passed through the heat treatmentapparatus) and a heat treatment temperature in the heat treatmentapparatus were set as seen in Table 6.

<Evaluating Peel Strength>

Next, a delamination test specimen having a width of 1.0 cm was producedfrom each of the produced metal-clad laminate sheets. A thermoplasticliquid crystal polymer film layer of the test specimen was fixed to aflat plate with double-sided adhesive tape. When the metal foil wasdelaminated in a 180°-peel test at a speed of 50 mm/min in compliancewith JISC5016, a strength (kN/m) was measured.

Note that in view of, for example, flex resistance, a delaminationstrength of 0.7 kN/m or higher was required. Hence the peel strength wasdetermined to be good when the strength was 0.7 kN/m or higher. Table 6shows the results.

<Measuring Insertion Loss>

Next an insertion loss was measured for each of the produced metal-cladlaminate sheets. More specifically, the insertion loss was measured witha microwave network analyzer (Manufactured by Agilent, Model: 8722ES)and a probe (Manufactured by Cascade Microtech, Inc., Model: ACP-250) ata frequency of 40 GHz.

Note that in view of high frequency characteristics, an insertion lossof −0.8 or below was determined to be good. An insertion loss of −0.8 orabove was determined to be poor. Table 6 shows the results.

Examples 11 to 13, Comparative Examples 7 to 9

The copper foil used had a thickness of 12 μm (Manufactured by MitsuiMining & Smelting Co., Ltd., Trade Name: TQ-M7-VSP, Surface Roughness:1.1 μm). Other than heat treatments provided at the temperatures for thetime periods shown in Table 7, metal-clad laminate sheets were producedin a similar manner as the above Example 1. Then, as seen in the aboveExample 1, peel strength was evaluated and insertion loss was measured.Table 7 shows the results.

Examples 14 to 16, Comparative Examples 10 to 12

The copper foil used had a thickness of 12 μm (JX Nippon Mining & MetalsCorporation, Trade Name: BHYX-92F-HA, Surface Roughness of Shiny Side:0.5 μm). Other than heat treatments provided at the temperatures for thetime periods shown in Table 8, metal-clad laminate sheets were producedin a similar manner as the above Example 1. Then, as seen in the aboveExample 1, peel strength was evaluated and insertion loss was measured.Table 8 shows the results.

Examples 17 to 19, Comparative Examples 13 and 14

<Producing Thermoplastic Liquid Crystal Polymer Film>

Thermotropic liquid crystal polyester containing a 6-hydroxy-2-naphthoicacid unit (27 mol %) and a p-hydroxybenzoic acid unit (73 mol %) washeated at 280° C. to 300° C. and kneaded with a single screw extruder.Then, the thermotropic liquid crystal polyester was extruded from aninflation die having a diameter of 40 mm and a slit distance of 0.6 mmso that thermoplastic liquid crystal polymer film having a thickness of50 μm was obtained. This thermoplastic liquid crystal polymer film has amelting point Tm of 283° C. and a heat distortion temperature Tdef of230° C.

A temperature of the surface of this thermoplastic liquid crystalpolymer film was raised to 260° C. in a hot air dryer with hot airhaving a temperature of 260° C. under a nitrogen atmosphere. Thethermoplastic liquid crystal polymer film was heat-treated at thistemperature for two hours. Then, the temperature was raised to 280° C.in 30 minutes. After that, the thermoplastic liquid crystal polymer filmwas heat-treated for two hours. After the heat treatment, thetemperature was lowered to 200° C. at a speed of 20° C./min. Then thethermoplastic liquid crystal polymer film was taken out of the hot airdryer. The obtained film had a melting point of 315° C.

Then, the copper foil used had a thickness of 12 μm (JX Nippon Mining &Metals Corporation, Trade Name: BHYX-92F-HA, Surface Roughness: 0.9 μm).Other than heat treatments provided at the temperatures for the timeperiods shown in Table 9, metal-clad laminate sheets were produced in asimilar manner as the above Example 1. Then, as seen in the aboveExample 1, peel strength was evaluated and insertion loss was measured.Table 9 shows the results.

Examples 20 to 26, Comparative Examples 15 to 18

Other than the use of a hot air circulation furnace (Manufactured byYamato Scientific Co., Ltd., Trade Name: Inert Oven DN4111) as a heattreatment unit instead of the infrared heat treatment apparatus, andheat treatments provided at the temperatures for the time periods shownin Table 10, metal-clad laminate sheets were produced in a similarmanner as the above Example 1. Then, as seen in the above Example 1,peel strength was evaluated and insertion loss was measured. Table 10shows the results.

Examples 27 to 29, Comparative Examples 19 and 20

Other than the use of the hot air circulation furnace (Manufactured byYamato Scientific Co., Ltd., Trade Name: Inert Oven DN411) as a heattreatment unit instead of the infrared heat treatment apparatus, andheat treatments provided at the temperatures for the time periods shownin Table 11, metal-clad laminate sheets were produced in a similarmanner as the above Example 11. Then, as seen in the above Example 1,peel strength was evaluated and insertion loss was measured. Table 11shows the results.

TABLE 6 Peel Strength Film Melting Heat Treatment between Copper PointTemperature Ta − Heat Treatment Surface Roughness Foil and Insertion Tm(° C.) Ta(° C.) Tm (° C.) Time (min) of Copper Foil (μm) Film(kN/m)Loss(db/cm) Example1 283 300 17 0.15 0.9 1.05 −0.62 Example2 283 300 171 0.9 1.3 −0.62 Example3 283 300 17 5 0.9 0.8 −0.62 Example4 283 290 70.15 0.9 1.05 −0.62 Example5 283 290 7 2 0.9 1.1 −0.62 Example6 283 2907 5 0.9 0.75 −0.62 Example7 283 285 2 0.15 0.9 0.8 −0.62 Example8 283285 2 0.5 0.9 1.05 −0.62 Example9 283 285 2 2 0.9 1.1 −0.62 Example10283 285 2 5 0.9 0.8 −0.62 Comparative 283 — — 0 0.9 0.325 −0.62 Example1Comparative 283 300 17 15 0.9 0.6 −0.62 Example2 Comparative 283 290 715 0.9 0.6 −0.62 Example3 Comparative 283 290 7 30 0.9 0.6 −0.62Example4 Comparative 283 285 2 15 0.9 0.6 −0.62 Example5 Comparative 283285 2 30 0.9 0.6 −0.62 Example6

TABLE 7 Peel Strength Film Melting Heat Treatment between Copper PointTemperature Ta − Heat Treatment Surface Roughness Foil and Insertion Tm(° C.) Ta(° C.) Tm (° C.) Time (min) of Copper Foil (μm) Film(kN/m)Loss(db/cm) Example11 283 290 7 0.5 1.1 1.25 −0.77 Example12 283 290 7 11.1 1.55 −0.77 Example13 283 290 7 5 1.1 0.75 −0.77 Comparative 283 — —0 1.1 0.4 −0.77 Example7 Comparative 283 290 7 15 1.1 0.55 −0.77Example8 Comparative 283 290 7 30 1.1 0.55 −0.77 Example9

TABLE 8 Peel Strength Film Melting Heat Treatment between Copper PointTemperature Ta − Heat Treatment Surface Roughness Foil and Insertion Tm(° C.) Ta(° C.) Tm (° C.) Time (min) of Copper Foil (μm) Film(kN/m)Loss(db/cm) Example14 283 290 7 0.15 0.5 0.9 −0.45 Example15 283 290 7 10.5 1 −0.45 Example16 283 290 7 5 0.5 0.95 −0.45 Comparative 283 — — 00.5 0.2 −0.45 Example10 Comparative 283 290 7 15 0.5 0.6 −0.45 Example11Comparative 283 290 7 30 0.5 0.6 −0.45 Example12

TABLE 9 Peel Strength Film Melting Heat Treatment between Copper PointTemperature Ta − Heat Treatment Surface Roughness Foil and Insertion Tm(° C.) Ta(° C.) Tm (° C.) Time (min) of Copper Foil (μm) Film(kN/m)Loss(db/cm) Example17 315 320 5 0.15 0.9 1.15 −0.62 Example18 315 320 51 0.9 1.4 −0.62 Example19 315 320 5 5 0.9 0.8 −0.62 Comparative 315 — —0 0.9 0.65 −0.62 Example13 Comparative 315 320 5 15 0.9 0.6 −0.62Example14

TABLE 10 Peel Strength Film Melting Heat Treatment between Copper PointTemperature Ta − Heat Treatment Surface Roughness Foil and Insertion Tm(° C.) Ta(° C.) Tm (° C.) Time (min) of Copper Foil (μm) Film(kN/m)Loss(db/cm) Example20 283 300 17 0.5 0.9 1.05 −0.62 Example21 283 300 171 0.9 1.3 −0.62 Example22 283 300 17 5 0.9 0.8 −0.62 Example23 283 290 72 0.9 1 −0.62 Example24 283 290 7 5 0.9 0.75 −0.62 Example25 283 285 2 20.9 0.7 −0.62 Example26 283 285 2 5 0.9 0.8 −0.62 Comparative 283 300 1715 0.9 0.65 −0.62 Example15 Comparative 283 290 7 30 0.9 0.6 −0.62Example16 Comparative 283 285 2 15 0.9 0.45 −0.62 Example17 Comparative283 285 2 30 0.9 0.5 −0.62 Example18

TABLE 11 Peel Strength Film Melting Heat Treatment between Copper PointTemperature Ta − Heat Treatment Surface Roughness Foil and Insertion Tm(° C.) Ta(° C.) Tm (° C.) Time (min) of Copper Foil (μm) Film(kN/m)Loss(db/cm) Example27 283 290 7 0.5 1.1 1.25 −0.77 Example28 283 290 7 11.1 1.25 −0.77 Example29 283 290 7 5 1.1 0.75 −0.77 Comparative 283 2907 15 1.1 0.55 −0.77 Example19 Comparative 283 290 7 30 1.1 0.55 −0.77Example20

As Tables 6 to 11 show, the heat treatment temperature Ta was set torange between 1° C. inclusive and 50° C. exclusive higher than themelting point Tm of the thermoplastic liquid crystal polymer film andthe heat treatment was provided for one second to 10 minutes in Examples1 to 29. Examples 1 to 29 show that the metal-clad laminate sheetsobtained have a high frequency characteristic and good peel strengthbetween a thermoplastic liquid crystal polymer film and metal foil.

Meanwhile, in Comparative Examples 1 to 20, either the heat treatmentwas not provided or was provided for an excessive time period. Comparedwith Examples 1 to 29, Comparative Examples 1 to 20 show poor peelstrength between a thermoplastic liquid crystal polymer film and metalfoil.

Examples 30 to 33, Comparative Example 21

<Producing Thermoplastic Liquid Crystal Polymer Film>

Thermotropic liquid crystal polyester containing a 6-hydroxy-2-naphthoicacid unit (27 mol %) and a p-hydroxybenzoic acid unit (73 mol %) washeated at 280° C. to 300° C. and kneaded with a single screw extruder.Then, the thermotropic liquid crystal polyester was extruded from aninflation die having a diameter of 40 mm and a slit distance of 0.6 mmso that thermoplastic liquid crystal polymer film having a thickness of50 μm was obtained. This thermoplastic liquid crystal polymer film has amelting point Tm of 282° C. and a heat distortion temperature Tdef of230° C.

Other than heat treatments provided at the temperatures for the timeperiods shown in Table 12, metal-clad laminate sheets were produced in asimilar manner as the above Example 1. Then, as seen in the aboveExample 1, peel strength was evaluated and insertion loss was measured.Table 12 shows the results.

<Measuring Coefficient of Thermal Expansion>

Using a thermal mechanical analyzer (TMA), a tensile force of 1 g wasapplied to both ends of the thermoplastic liquid crystal polymer filmhaving a width of S mm and a length of 20 mm. A temperature of the filmwas raised from a room temperature to 200° C. at a speed of 5° C./min,and a coefficient of thermal expansion of the film was measured based ona variation in film length between 30° C. and 150° C. Table 12 shows theresults.

<Measuring Thickness of Skin Layer>

Next, each of the produced metal-clad laminate sheets was embedded inacrylic resin. The cross section of the metal-clad laminate sheet waspolished with a cross-section polisher and etched with a propylaminesolution so that the structure of the domains was emphasized. The crosssection was then observed with a scanning electron microscope (SEM). Anaverage value of thicknesses of any given five portions of a skin layerwas calculated within an area of 30μ×30 μm observed in a cross-sectionimage.

<Evaluating Dimensional Stability>

Next, for the produced copper-clad laminate sheets, a rate of variationin dimension (%) in the MD and TD directions was measured in compliancewith IPC-TM-6502.2.4. An average value of the rates of variation wasdetermined as a dimensional variation. When the dimensional variation isnot over ±0.1%, the dimensional stability is good. Table 12 shows theresults.

TABLE 12 Peel Heat Coefficient Strength Film Treatment Surface ofThermal between Melting Temper- Heat Roughness Expansion CopperThickness Dimensional Point ature Ta − Treatment of Copper of Film (ppm/Foil and Insertion of Skin Variation Tm (° C.) Ta(° C.) Tm (° C.) Time(min) Foil (μm) ° C.) Film(kN/m) Loss(db/cm) layer(μm) (%) Example 30282 300 18 0.15 0.9 10 1.0 −0.62 Equal to 0.1 Surface Roughness ofCopper foil or Smaller Example 31 282 300 18 1 0.9 18 1.0 −0.62 Equal to0.03 Surface Roughness of Copper foil or Smaller Example 32 282 300 18 20.9 21 1.0 −0.62 Equal to 0.05 Surface Roughness of Copper foil orSmaller Example 33 282 300 18 3 0.9 30 1.0 −0.62 Equal to 0.1 SurfaceRoughness of Copper foil or Smaller Comparative 282 270 −12 1 0.9 −7 0.4−0.62 4 0.15 Example21

As Table 12 shows, the heat treatment temperature Ta was set to rangebetween 1° C. inclusive and 50° C. exclusive higher than the meltingpoint Tm of the thermoplastic liquid crystal polymer film and the heattreatment was provided for one second to 10 minutes in Examples 30 to33. Examples 30 to 33 show that the metal-clad laminate sheets obtainedhave a high frequency characteristic and increased peel strength betweena thermoplastic liquid crystal polymer film and metal foil.

More specifically, in Example 30, for example, FIG. 12 shows the skinlayer 16 on the surface of the core layer 17 of the metal-clad laminatesheet before heat treatment. However, in FIG. 13, the skin layer 16 hasdisappeared from the metal-clad laminate sheet after heat treatment,showing an increase in the peel strength between the metal foil (copperfoil) 3 and the core layer 17. Moreover, also in Examples 31 to 33, theskin layer has disappeared as has done so in Example 30, showing anincrease in peel strength between a metal foil (copper foil) and a corelayer.

Meanwhile, in Comparative Example 21, the heat treatment was provided ata temperature lower than the melting point of the thermoplastic liquidcrystal polymer film, such that the skin layer has not disappeared.Compared with Examples 30 to 33, Comparative Example 21 shows poor peelstrength between the thermoplastic liquid crystal polymer film and themetal foil.

Compared with Comparative Example 21, Examples 30 to 33 show adimensional variation of not over ±0.1%, showing good dimensionalstability.

Examples 34 to 43, Comparative Examples 22 to 27

<Producing Thermoplastic Liquid Crystal Polymer Film>

Thermotropic liquid crystal polyester containing a 6-hydroxy-2-naphthoicacid unit (27 mol %) and a p-hydroxybenzoic acid unit (73 mol %) washeated at 280° C. to 300° C. and kneaded with a single screw extruder.Then, the thermotropic liquid crystal polyester was extruded from aninflation die having a diameter of 40 mm and a slit distance of 0.6 mmso that a thermoplastic liquid crystal polymer film 2 having a thicknessof 50 μm was obtained. This thermoplastic liquid crystal polymer filmhas a melting point Tm of 283° C. and a heat distortion temperature Tdefof 230° C.

Note that the melting point was obtained with a differential scanningcalorimeter through an observation of a thermal behavior of the film.Specifically, the produced film was heated at a speed of 20° C./min tomelt completely. Then, the melt film was rapidly cooled to 50° C. at aspeed of 50° C./min. Then, when the cooled film was heated again at aspeed of 20° C./min, the endothermic peak observed was determined as themelting point of the thermoplastic liquid crystal polymer film.

<Producing Single-Sided Metal-Clad Laminate Sheet>

Next, using a continuous hot-press apparatus, the produced thermoplasticliquid crystal polymer film and, as the metal foil 3, rolled copper foilhaving a thickness of 12 μm (Manufactured by JX Nippon Mining & MetalsCorporation, Trade Name: BHYX-92F-HA, Surface Roughness: 0.9 μm) wereintroduced between a heat-resistant rubber roll and a heating metalroll, and thermally pressed to bond together. Hence, a laminate sheetwas produced.

Note that the surface roughness Rz of the copper foil was calculatedthrough measurement of ten point average surface roughness on aroughened face in compliance with JISB0601, using a surface roughnesstester (Manufactured by Mitsutoyo Corporation, Trade Name: SURF TESTSJ-201). Under a condition in which a measurement reference length was0.8 mm, an evaluation length was 4 mm, a cutoff value was 0.8 mm, and afeed speed was 0.5 mm/sec, the surface roughness was measured 10 timeswith the measurement position changed to be in parallel with the rollingdirection. An average value among the ten measurements was obtained.

As the heat-resistant rubber roll making contact with the thermoplasticliquid crystal polymer film, a resin-coated metal roll (Manufactured byYuri Roll Machine Co., Ltd., Trade Name: Super Ten Apex. ResinThickness: 1.7 cm) was used. The heat-resistant rubber roll and theheating metal roll used had a diameter of 40 cm.

A surface temperature of the heating metal roll was set to a temperature20° C. lower (i.e., 263° C.) than the melting point of the thermoplasticliquid crystal polymer film. A pressure to be applied to thethermoplastic liquid crystal polymer film and the copper foil betweenthe heat-resistant rubber roll and the heating metal roll was set to 120kg/cm² in face pressure. Under this condition, the thermoplastic liquidcrystal polymer film was moved along the heat-resistant rubber roll.Then, the copper foil was laid on, and temporarily bonded to, thethermoplastic liquid crystal polymer film.

<Heat Treading>

Next, winding tension was released on the production line with a niproll. The produced laminate sheet was passed through an infrared heattreatment apparatus (Manufactured by Noritake Co., Ltd., Trade Name:Roll to Roll Far-Infrared Heating Furnace) as a heat treatment unit, andheat-treated. Single-sided metal-clad laminate sheets for Examples 34 to43 and Comparative Examples 22 to 27 were produced.

Note that a heat treatment time (i.e., a time period in which any givenone point of a laminate sheet passed through the heat treatmentapparatus) and a heat treatment temperature in the heat treatmentapparatus were set as seen in Table 13.

<Producing Circuit Board>

Next, the circuit board 36 was produced. More specifically, thermotropicliquid crystal polyester containing a 6-hydroxy-2-naphthoic acid unit(27 mol %) and a p-hydroxybenzoic acid unit (73 mol %) was heated at280° C. to 300° C. and kneaded with a single screw extruder. Then, thethermotropic liquid crystal polyester was extruded from an inflation diehaving a diameter of 40 mm and a slit distance of 0.6 mm so thatthermoplastic liquid crystal polymer film having a thickness of 50 μmwas obtained. This thermoplastic liquid crystal polymer film has amelting point Tm of 283° C. and a heat distortion temperature Tdef of230° C.

A temperature of the surface of this thermoplastic liquid crystalpolymer film was raised to 260° C. in a hot air dryer with hot airhaving a temperature of 260° C. under a nitrogen atmosphere. Thethermoplastic liquid crystal polymer film was heat-treated at thistemperature for two hours. Then, the temperature was raised to 280° C.in 30 minutes. After that, the thermoplastic liquid crystal polymer filmwas heat-treated for two hours. After the heat treatment, thetemperature was lowered to 200° C. at a speed of 20° C./min. Then thethermoplastic liquid crystal polymer film was taken out of the hot airdryer. The obtained film had a melting point of 315° C.

Rolled copper foil having a thickness of 12 μm (Manufactured by JXNippon Mining & Metals Corporation, Trade Name: BHYX-92F-HA, SurfaceRoughness: 0.9 μm) was pressed on, and attached to, each side of thisfilm with vacuum batch-press machine (Manufactured by Kitagawa SeikiCo., Ltd. Trade Name: VH2-1600) at 4 Torr, at 300° C., for 10 minutes.Hence, a double-sided metal-clad laminate sheet was produced. Then, thecircuit pattern 37 was patterned on one face of the copper foil with aphotomask so that the circuit board 36 was produced.

<Producing Multilayer Circuit Board>

Next, the multilayer circuit boards 38, 60, and 61 were produced asrespectively shown in FIGS. 6, 9, and 11.

More specifically, as illustrated in FIG. 7, the single-sided metal-cladlaminate sheet 1 and the circuit board 36 were laid on top of the otherand laminated together via (i) the film face 35 of the single-sidedmetal-clad laminate sheet 1, (ii) the surface 40, of the thermoplasticliquid crystal polymer film 2, across from the metal foil 3 in thecircuit board 36, and (iii) the surface 27 of the circuit pattern 37 inthe circuit board 36. With a vacuum batch-press machine (Manufactured byKitagawa Seiki Co., Ltd. Trade Name: VH2-1600), this laminate was heatedand pressed for 15 minutes (under the following condition: at a pressureof 4 Torr, at a temperature of 290° C., and at a pressure of 1.5 Mpa) byvacuum hot pressing so that the single-sided metal-clad laminate sheet 1and the circuit board 36 were thermocompression-bonded together. As aresult, the multilayer circuit board 38 was produced as illustrated inFIG. 6.

Moreover, as illustrated in FIG. 8, two single-sided metal-clad laminatesheets 1 were laminated together via the film faces 35 of theirrespective single-sided metal-clad laminate sheets 1. With a vacuumbatch-press machine (Manufactured by Kitagawa Seiki Co., Ltd. TradeName: VH2-1600), this laminate was heated and pressed for 15 minutes(under the following condition: at a pressure of 4 Tort, at atemperature of 290° C., and at a pressure of 1.5 Mpa) by vacuum hotpressing so that the two single-sided metal-clad laminate sheets 1 werethermocompression-bonded together. As a result, the multilayer circuitboard 60 was produced as illustrated in FIG. 9.

Moreover, as the film substrate 25 illustrated in FIG. 10, thethermoplastic liquid crystal polymer film 2 included in the abovesingle-sided metal-clad laminate sheet 1 was prepared. The single-sidedmetal-clad laminate sheet 1 and the film substrate 25 were laid on topof the other and laminated together via (i) the film face 35 of thesingle-sided metal-clad laminate sheet 1, and (ii) the film face 26 ofthe film substrate 25. With a vacuum batch-press machine (Manufacturedby Kitagawa Seiki Co., Ltd. Trade Name: VH2-1600), this laminate washeated and pressed for 15 minutes (under the following condition: at apressure of 4 Torr, at a temperature of 290° C., and at a pressure of1.5 Mpa) by vacuum hot pressing so that the single-sided metal-cladlaminate sheet 1 and the film substrate 25 were thermocompression-bondedtogether. As a result, the multilayer circuit board 61 was produced asillustrated in FIG. 11.

<Evaluating Peel Strength>

Next, a delamination test specimen having a width of 1.0 cm was producedfrom the produced single-sided metal-clad laminate sheet 1. The testspecimen was fixed to a flat plate with double-sided adhesive tape.Next, when the metal foil (the copper foil) 3 was delaminated in a180°-peel test at a speed of 50 mm/min in compliance with JISC5016, astrength (kN/m) was measured for the interface 34 between thethermoplastic liquid crystal polymer film 2 and the metal foil 3 in thesingle-sided metal-clad laminate sheet 1.

In a similar manner, a delamination test specimen having a width of 1.0cm was produced from the multilayer circuit board 38. The test specimenwas fixed to a flat plate with double-sided adhesive tape. When thesingle-sided metal-clad laminate sheet 1 was delaminated in a 180°-peeltest at a speed of 50 mm/min in compliance with JISC5016, a strength(kN/m) was measured for the interface 50 between the thermoplasticliquid crystal polymer film 2 and the circuit pattern 37 of the circuitboard 36. Note that the peel strength was separately measured (i)between the film face 35 of the single-sided metal-clad laminate sheet 1and the surface 40, of the thermoplastic liquid crystal polymer film 2,across from the metal foil 3 in the circuit board 36, and (ii) betweenthe film face 35 of the single-sided metal-clad laminate sheet 1 and thesurface 27 of the circuit pattern 37 in the circuit board 36.

Moreover, in a similar manner, a delamination test specimen having awidth of 1.0 cm was produced from the multilayer circuit boards 60 and61. Each test specimen was fixed to a flat plate with double-sidedadhesive tape. Then, when the thermoplastic liquid crystal polymer film2 was delaminated in a 180°-peel test at a speed of 50 mm/min incompliance with JISC5016, a strength (kN/m) was measured for (i) aninterface 71 between the thermoplastic liquid crystal polymer films 2 ofthe respective single-sided metal-clad laminate sheets 1 for themultilayer circuit board 60, and (ii) the interface 23 between thethermoplastic liquid crystal polymer film 2 in the single-sidedmetal-clad laminate sheet 1 and the thermoplastic liquid crystal polymerfilm 2 of the film substrate 25 for the multilayer circuit board 61.

Note that in view of, for example, flex resistance, a delaminationstrength of 0.7 kN/m or higher was required. Hence the peel strength wasdetermined to be good when the strength was 0.7 kN/m or higher for eachpeel strength evaluation. Table 13 shows the results.

<Measuring Insertion Loss>

Next an insertion loss was measured for each of the single-sidedmetal-clad laminate sheets 1. More specifically, the insertion loss wasmeasured with a microwave network analyzer (Manufactured by Agilent,Model: 8722ES) and a probe (Manufactured by Cascade Microtech, Inc.,Model: ACP-250) at a frequency of 40 GHz.

Note that in view of high frequency characteristics, an insertion lossof −0.8 or below was determined to be good. An insertion loss of −0.8 orabove was determined to be poor. Table 13 shows the results.

Examples 44 to 46, Comparative Examples 28 to 30

The copper foil used had a thickness of 12 μm (Manufactured by MitsuiMining & Smelting Co., Ltd., Trade Name: TQ-M7-VSP, Surface Roughness:1.1 μm). Other than heat treatments provided at the temperatures for thetime periods shown in Table 14, single-sided metal-clad laminate sheetsand multilayer circuit boards were produced in a similar manner as theabove Example 1. Then, as seen in the above Example 1, peel strength wasevaluated and insertion loss was measured. Table 14 shows the results.

Examples 47 to 49, Comparative Examples 31 to 33

The copper foil used had a thickness of 12 μm (JX Nippon Mining & MetalsCorporation, Trade Name: BHYX-92F-HA, Surface Roughness of Shiny Side:0.5 μm). Other than heat treatments provided at the temperatures for thetime periods shown in Table 15, single-sided metal-clad laminate sheetand multilayer circuit board were produced in a similar manner as theabove Example 1. Then, as seen in the above Example 1, peel strength wasevaluated and insertion loss was measured. Table 15 shows the results.

Examples 50 to 52, Comparative Examples 34 to 36

<Producing Thermoplastic Liquid Crystal Polymer Film>

Thermotropic liquid crystal polyester containing a 6-hydroxy-2-naphthoicacid unit (27 mol %) and a p-hydroxybenzoic acid unit (73 mol %) washeated at 280° C. to 300° C. and kneaded with a single screw extruder.Then, the thermotropic liquid crystal polyester was extruded from aninflation die having a diameter of 40 mm and a slit distance of 0.6 mmso that thermoplastic liquid crystal polymer film having a thickness of50 μm was obtained. This thermoplastic liquid crystal polymer film has amelting point Tm of 283° C. and a heat distortion temperature Tdef of230° C.

A temperature of the surface of this thermoplastic liquid crystalpolymer film was raised to 260° C. in a hot air dryer with hot airhaving a temperature of 260° C. under a nitrogen atmosphere. Thethermoplastic liquid crystal polymer film was heat-treated at thistemperature for two hours. Then, the temperature was raised to 280° C.in 30 minutes. After that, the thermoplastic liquid crystal polymer filmwas heat-treated for two hours. After the heat treatment, thetemperature was lowered to 200° C. at a speed of 20° C./min. Then thethermoplastic liquid crystal polymer film was taken out of the hot airdryer. The obtained film had a melting point of 315° C.

Then, the copper foil having a thickness of 12 μm (JX Nippon Mining &Metals Corporation, Trade Name: BHYX-92F-HA, Surface Roughness: 0.9 μm)was used. Peel strength was evaluated and insertion loss was measured asseen in the above Example 1, other than producing single-sidedmetal-clad laminate sheets through heat treatments provided at thetemperatures for the time periods shown in Table 16, and setting atemperature to 305° C. for thermocompression bonding for laminating eachof the single-sided metal-clad laminate sheets. Table 16 shows theresults.

Examples 53 to 59, Comparative Examples 37 to 40

Single-sided metal-clad laminate sheets and multilayer circuit boardswere produced in a similar manner as described in the above Example 1,other than the use of a hot air circulation furnace (Manufactured byYamato Scientific Co., Ltd., Trade Name: Inert Oven DN4111) as a heattreatment unit instead of the infrared heat treatment apparatus, andheat treatments provided at the temperatures for the time periods shownin Table 17. Then, as seen in the above Example 1, peel strength wasevaluated and insertion loss was measured. Table 17 shows the results.

TABLE 13 Film Heat Surface Interface 34: Melting Treatment HeatRoughness Peel Strength Point Temperature Ta − Treatment of Copperbetween Copper Tm(° C.) Ta(° C.) Tm (° C.) Time (min) Foil (μm) Foil andFilm (kN/m) Example34 283 300 17 0.15 0.9 1.05 Example35 283 300 17 10.9 1.3 Example36 283 300 17 5 0.9 0.8 Example37 283 290 7 0.15 0.9 1.05Example38 283 290 7 2 0.9 1.1 Example39 283 290 7 5 0.9 0.75 Example40283 285 2 0.15 0.9 0.8 Example41 283 285 2 0.5 0.9 1.05 Example42 283285 2 2 0.9 1.1 Example43 283 285 2 5 0.9 0.8 Comparative 283 — — 0 0.90.325 Example 22 Comparative 283 300 17 15 0.9 0.6 Example 23Comparative 283 290 7 15 0.9 0.6 Example 24 Comparative 283 290 7 30 0.90.6 Example 25 Comparative 283 285 2 15 0.9 0.6 Example 26 Comparative283 285 2 30 0.9 0.6 Example 27 Peel Strength in Multilayer CircuitBoard(kN/m) Interface 50: Interface 50: Peel Strength Peel Strengthbetween Film between Film Face 35 and Face 35 and Surface 27 Surface 40Interface 71: Interface 23: Insertion of Circuit across from PeelStrength Peel Strength Loss (db/cm) Pattern 37 Metal Foil 3 betweenFilms between Films Example34 −0.62 0.9 1.1 1.3 1.1 Example35 −0.62 0.71.1 1.3 1.0 Example36 −0.62 0.7 0.9 1.1 1.0 Example37 −0.62 0.9 1.1 1.21.1 Example38 −0.62 0.8 1.1 1.2 1.0 Example39 −0.62 0.7 0.9 1.0 1.1Example40 −0.62 0.9 1.2 1.2 1.1 Example41 −0.62 0.8 1.1 1.2 1.0Example42 −0.62 0.7 1.1 1.2 1.1 Example43 −0.62 0.7 1.0 1.1 1.0Comparative −0.62 0.4 0.3 0.4 0.5 Example 22 Comparative −0.62 1.0 0.50.6 0.6 Example 23 Comparative −0.62 1.0 0.6 0.7 0.7 Example 24Comparative −0.62 1.0 0.5 0.5 0.6 Example 25 Comparative −0.62 0.9 0.60.7 0.7 Example 26 Comparative −0.62 0.9 0.6 0.6 0.6 Example 27

TABLE 14 Film Heat Surface Interface 34: Melting Treatment HeatRoughness Peel Strength Point Temperature Ta − Treatment of Copperbetween Copper Tm(° C.) Ta(° C.) Tm (° C.) Time (min) Foil (μm) Foil andFilm (kN/m) Example 44 283 290 7 0.15 1.1 1.25 Example 45 283 290 7 11.1 1.55 Example 46 233 290 7 5 1.1 0.75 Comparative 283 — — 0 1.1 0.4Example 28 Comparative 283 290 7 15 1.1 0.55 Example 29 Comparative 283290 7 30 1.1 0.55 Example 30 Peel Strength in Multilayer CircuitBoard(kN/m) Interface 50: Interface 50: Peel Strength Peel Strengthbetween Film between Film Face 35 and Face 35 and Surface 27 Surface 40Interface 71: Interface 23: Insertion of Circuit across from PeelStrength Peel Strength Loss (db/cm) Pattern 37 Metal Foil 3 betweenFilms between Films Example 44 −0.77 0.9 1.1 1.3 1.1 Example 45 −0.770.7 1.1 1.3 1.0 Example 46 −0.77 0.7 0.9 1.1 1.0 Comparative −0.77 0.40.3 0.4 0.5 Example 28 Comparative −0.77 0.8 0.9 1.2 1.0 Example 29Comparative −0.77 0.8 0.8 1.2 0.9 Example 30

TABLE 15 Film Heat Surface Interface 34: Melting Treatment HeatRoughness Peel Strength Point Temperature Ta − Treatment of Copperbetween Copper Tm(° C.) Ta(° C.) Tm (° C.) Time (min) Foil (μm) Foil andFilm (kN/m) Example47 283 290 7 0.15 0.5 0.9 Example48 283 290 7 1 0.5 1Example49 283 290 7 5 0.5 0.95 Comparative 283 — — 0 0.5 0.2 Example 31Comparative 283 290 7 15 0.5 0.6 Example 32 Comparative 283 290 7 30 0.50.6 Example 33 Peel Strength in Multilayer Circuit Board(kN/m) Interface50: Interface 50: Peel Strength Peel Strength between Film between FilmFace 35 and Face 35 and Surface 27 Surface 40 Interface 71: Interface23: Insertion of Circuit across from Peel Strength Peel Strength Loss(db/cm) Pattern 37 Metal Foil 3 between Films between Films Example47−0.4 0.9 1.2 1.3 1.1 Example48 −0.4 0.7 1.2 1.3 1.0 Example49 −0.4 0.71.1 1.1 1.0 Comparative −0.4 0.4 0.3 0.4 0.5 Example 31 Comparative −0.40.8 0.9 1.2 1.0 Example 32 Comparative −0.4 0.8 0.8 1.2 0.9 Example 33

TABLE 16 Film Heat Surface Interface 34: Melting Treatment HeatRoughness Peel Strength Point Temperature Ta − Treatment of Copperbetween Copper Tm(° C.) Ta(° C.) Tm (° C.) Time (min) Foil (μm) Foil andFilm (kN/m) Example50 315 320 5 0.15 0.9 0.9 Example51 315 320 5 1 0.9 1Example52 315 320 5 5 0.9 0.95 Comparative 315 — — 0 0.9 0.2 Example 34Comparative 315 320 5 15 0.9 0.6 Example 35 Comparative 315 320 5 30 0.90.6 Example 36 Peel Strength in Multilayer Circuit Board(kN/m) Interface50: Interface 50: Peel Strength Peel Strength between Film between FilmFace 35 and Face 35 and Surface 27 Surface 40 Interface 71: Interface23: Insertion of Circuit across from Peel Strength Peel Strength Loss(db/cm) Pattern 37 Metal Foil 3 between Films between Films Example50−0.62 0.8 1.1 1.2 1.0 Example51 −0.62 0.7 1.1 1.2 0.9 Example52 −0.620.7 0.9 1.0 0.9 Comparative −0.62 0.2 0.4 0.4 0.5 Example 34 Comparative−0.62 0.5 0.8 1.0 0.8 Example 35 Comparative −0.62 0.5 0.7 1.0 0.7Example 36

TABLE 17 Film Heat Surface Interface 34: Melting Treatment HeatRoughness Peel Strength Point Temperature Ta − Treatment of Copperbetween Copper Tm(° C.) Ta(° C.) Tm (° C.) Time (min) Foil (μm) Foil andFilm (kN/m) Example53 283 300 17 0.5 0.9 1.05 Example54 283 300 17 1 0.91.3 Example55 283 300 17 5 0.9 0.8 Example56 283 290 7 2 0.9 1 Example57283 290 7 5 0.9 0.75 Example58 283 285 2 2 0.9 0.7 Example59 283 285 2 50.9 0.3 Comparative 283 300 17 15 0.9 0.65 Example 37 Comparative 283290 7 30 0.9 0.6 Example 38 Comparative 283 285 2 15 0.9 0.45 Example 39Comparative 283 285 2 30 0.9 0.5 Example 40 Peel Strength in MultilayerCircuit Board(kN/m) Interface 50: Interface 50: Peel Strength PeelStrength between Film between Film Face 35 and Face 35 and Surface 27Surface 40 Interface 71: Interface 23: Insertion of Circuit across fromPeel Strength Peel Strength Loss (db/cm) Pattern 37 Metal Foil 3 betweenFilms between Films Example53 −0.62 0.9 1.1 1.3 1.1 Example54 −0.62 0.81.2 1.3 1.0 Example55 −0.62 0.8 1 1.1 1.0 Example56 −0.62 0.8 1.1 1.21.1 Example57 −0.62 0.8 1.1 1.2 1.0 Example58 −0.62 0.7 1 1.0 1.1Example59 −0.62 0.7 1.2 1.2 1.1 Comparative −0.62 0.8 0.6 0.5 0.6Example 37 Comparative −0.62 0.8 0.6 0.7 0.6 Example 38 Comparative−0.62 0.7 0.7 0.6 0.6 Example 39 Comparative −0.62 0.7 0.6 0.7 0.6Example 40

The single-sided metal-clad laminate sheet 1 was produced in Examples 34to 59 through the heat treatment in which the heat treatment temperatureTa was set to range between 1° C. inclusive and 50° C. exclusive higherthan the melting point Tm of the thermoplastic liquid crystal polymerfilm, and the heat treatment was provided for one second to 10 minutes.Tables 13 to 17 show that such a single-sided metal-clad laminate sheet1 has a high frequency characteristic, and an peel strength of 0.7 kN/mor higher at the interface 34 between the thermoplastic liquid crystalpolymer film and the metal foil and at the interfaces 50, 71, and 23between the single-sided metal-clad laminate sheet 1 and anothersubstrate. Using the single-sided metal-clad laminate sheet 1, theobtained multilayer circuit boards 38, 60, and 61 excel in peel strengthand high frequency characteristic.

Meanwhile, the single-sided metal-clad laminate sheets used inComparative Examples 22 to 40 had either no heat treatment or a heattreatment over 10 minutes. As a result, the peel strength is lower than0.7 kN/m at the interface between a thermoplastic liquid crystal polymerfilm and a metal foil, and a portion of the peel strength is lower than0.7 kN/m between a film face and another substrate.

Suppose such a single-sided metal-clad laminate sheet having low peelstrength at an interface is used. Even though the peel strength betweena film face and another substrate is assumed to be 0.7 kN/m or higher,the single-sided metal-clad laminate sheet itself is not sufficientlystrong, and thus cannot withstand processing. Hence, this single-sidedmetal-clad laminate sheet has no practical use.

INDUSTRIAL APPLICABILITY

As described above, the present invention relates to a method formanufacturing a metal-clad laminate sheet including thermoplastic liquidcrystal polymer film. The present invention also relates to a metal-cladlaminate sheet manufactured by this method.

DESCRIPTION OF REFERENCE CHARACTERS

-   1 Metal-Clad Laminate Sheet-   2 Thermoplastic Liquid Crystal Polymer Film-   3 Metal Foil (metal foil)-   4 Delivery Roll-   5 Delivery Roll-   6 Laminate Sheet-   7 Heating Roll-   8 Heat-Resistant Rubber Roll-   9 Heating Metal Roll-   10 Continuous Hot-Press Apparatus-   11 Nip Roll-   12 Heat Treatment Unit-   13 Wind-Up Roll-   15 Laminate Sheet-   20 Metal-Clad Laminate Sheet-   25 Film Substrate-   30 Continuous Hot-Press Apparatus-   36 Circuit Board-   38 Multilayer Circuit Board-   60 Multilayer Circuit Board-   61 Multilayer Circuit Board

1-6. (canceled) 7: A method for manufacturing a multilayer circuit boardcomprising a single-sided metal-clad laminate sheet and a substratelaminated together, the single-sided metal-clad laminate sheetcomprising a thermoplastic liquid crystal polymer film and a metal foilbonded to a surface of the thermoplastic liquid crystal polymer film,and the method comprising: forming a laminate sheet having thethermoplastic liquid crystal polymer film and the metal foil bondedtogether; and heat treating the laminate sheet, wherein the heattreatment satisfies conditions (1) and (2) to manufacture thesingle-sided metal-clad laminate sheet: (1) a heat treatment temperatureranges between 1° C. inclusive and 50° C. exclusive higher than amelting point of the thermoplastic liquid crystal polymer film, and (2)a time for the heat treatment ranges from one second to 10 minutes. 8:The method of claim 7, wherein the metal foil has a low roughness. 9:The method of claim 7, wherein the multilayer circuit board furthercomprises another single-sided metal-clad laminate sheet, a substratehaving a circuit pattern, or a film substrate.